1. Technical Field
The present invention relates to a semiconductor device package, and more particularly, to a semiconductor device package capable of reducing occurrences of faulty welding of a package base to a lid or a seal ring to be joined thereto.
2. Related Art
A semiconductor device is sealed within a package, so as to be available for use. Typically, a semiconductor device package is comprised of a metal base having a placement section on which a semiconductor device is placed, a metal frame joined to the base, a seal ring joined to an open upper face of the frame, and a metal lid joined to the seal ring. The package is formed into a box-like shape as a whole. To hermetically seal a semiconductor device within such a package, the metal lid is seam-welded to the seal ring after the semiconductor device is received in a package housing formed by the metal base, metal frame and seal ring which are silver-brazed with one another.
In the seam welding, two roller electrodes are positioned individually at one ends of two facing sides of the metal lid, with the metal frame held on the seal ring of the package housing, and the roller electrodes are pressed against the metal lid. Thereafter, the roller electrodes and the package are moved relative to one another until the roller electrodes reach the other ends of the two sides of the metal lid, while a welding current is supplied between the electrodes, whereby the lid is seam-welded at the two sides to the seal ring. Then, the remaining two sides of the lid are seam-welded to the seal ring, thereby sealing the semiconductor device within the package. As for a package not provided with a seal ring, the metal lid is seam-welded to the metal frame.
As described above, a semiconductor device package is formed into a box-like shape as a whole. In other words, the package has four corners. Seam welding of the seal ring or the metal lid to the metal frame is carried out in such a manner that only a plated layer formed in advance on a surface of the seal ring or the metal lid is caused to melt, with a constituent material of the seal ring or the lid unmelted. Therefore, seam welding is advantageous in that it can reduce influences of welding heat upon a semiconductor device received in a package. On the other hand, unstable welding conditions are liable to occur at corners of a package, and in this case, faulty welding may be caused at the corners.
Although occurrences of such faulty welding can be reduced by increasing an amount of power supply to roller electrodes, welding heat increases with increase in the amount of power supply, so that a semiconductor device accommodated in a package may receive thermal affection, causing a misalignment in the semiconductor device. As for an optical semiconductor device and an optical component that are especially required of a high alignment accuracy, a misalignment can occur for such a simple reason that a creep deformation is caused in a silver alloy, with which various portions of an optical semiconductor device are joined to one another. Thus, an increased amount of power supply in seam welding for an optical semiconductor device package may cause a misalignment in an optical semiconductor device or an optical component received therein. This indicates that it is unpractical to increase the power supply amount to eliminate welding failure. Since seam welding for a semiconductor device package is carried out in a final stage of production of semiconductor modules, welding failure entails great damage, and therefore, a reduction of occurrences of faulty welding has been strongly demanded.
An object of the present invention is to provide a semiconductor device package capable of reducing occurrences of faulty welding, without the need of increasing an amount of power supply for seam welding of a metal base to a metal lid or a seal ring of the package.
According to one aspect of the present invention, there is provided a semiconductor device package comprised of a metal base having a placement section on which a semiconductor device is placed; a metal frame having a rectangular shape in transverse cross section and having a first face thereof joined to the metal base; and a metal lid joined to a second face of the metal frame. In the semiconductor device package, the second face of the metal frame is shaped, at its at least two sides facing each other out of four sides thereof, so as to be warped concavely toward the metal lid as viewed in vertical cross section, and the maximum warpage of the second face of the metal frame at each of the at least two sides is equal to or less than 0.2% of the length of the side of the second face.
Unlike a conventional package including a metal frame whose face (second face) on the metal-lid side is completely flat, the metal frame of the package of this invention has the second face thereof formed into a concave shape at its at least two facing sides. In other words, out of four wall portions that form the metal frame, at least two facing wall portions have metal-lid side faces that are formed into a concave shape. When the metal lid is brought in close contact with the metal frame, peripheral edge portions of the metal lid are slightly curved along the concave face of the metal frame. Hence, such a restoration force is generated in the peripheral edge portions of the metal lid as to restore the edge portions into an original straight shape, so that corner portions of the metal lid act to press the metal frame. In other words, at each corner of the package, the degree of close contact between the metal frame and the metal lid is enhanced. On the other hand, at the middle of adjacent corners of the metal lid (i.e., a central portion of a respective side (i.e., a respective peripheral edge) of the metal lid), the restoration force causes the metal lid to separate away from the concave face of the metal frame, incurring a possibility that the degree of close contact therebetween is lowered. In this invention, the maximum warpage of the concave face of the metal frame is limited to be equal to or less than 0.2% of the length of the concave side (i.e., concave face) of the metal frame, thereby preventing a reduction in the degree of contact between the metal lid and the metal frame at respective corners of the package. This makes it possible to enhance the degree of close contact between the metal lid and the metal frame at respective corners, while maintaining the metal lid and the metal frame in close contact with each other at the middle of adjacent corners of the package. Thus, welding conditions are stabilized along the entire periphery of the metal lid and the metal frame, whereby faulty welding can be reduced without the need of increasing an amount of power supply in seam welding.
According to another aspect of the present invention, there is provided a semiconductor device package comprised of a metal base having a placement section on which a semiconductor device is placed; a metal frame having a rectangular shape in transverse cross section and having a first face thereof joined to the metal base; a seal ring having a first face thereof joined to a second face of the metal frame; and a metal lid joined to a second face of the seal ring. In the semiconductor device package, the second face of the seal ring is shaped, at its at least two sides facing each other out of four sides thereof, so as to be warped concavely toward the metal lid as viewed in vertical cross section, and the maximum warpage of the second face of the seal ring at each of the at least two sides is equal to or less than 0.2% of the length of the side of the second face.
In this semiconductor device package, when the metal lid is brought in close contact with the seal ring, peripheral edge portions of the metal lid are slightly curved along the concave face of the seal ring, so that corner portions of the metal lid act to press the seal ring. Further, the maximum warpage at a respective side of the concave face of the seal ring is limited to a value not more than 0.2% of the length of the side, so that the metal lid and the seal ring are brought in close contact with each other over the entire periphery thereof, to thereby enhance the degree of close contact therebetween at respective corners of the package. As a result, welding conditions are stabilized along the entire periphery of the metal lid and the seal ring, whereby faulty welding can be reduced without the need of increasing an amount of power supply in seam welding.